1. Field of the Invention
The present invention relates generally to a diaphragm pump system for delivering small volumes of liquids, and more particularly to an air operated diaphragm pump system that employs fluid logic circuitry to drive a diaphragm pump submerged within the liquid to be discharged.
2. Prior Art
The need to (1) effectively drain all of the fluid present in a storage drum, or other vessel, and to (2) discharge same at a constant rate, is a frequently occurring problem arising in diverse industrial situations. One conventional solution of this problem is to employ a reciprocating displacement pump. Such pump is secured to the storage vessel above the liquid level, and a conduit depends below the pump into the liquid. Electrical or hydraulic control signals are supplied to an operator for the pump, and the pump functions to draw fluid upwardly through the conduit and discharge same through an outlet port. One representative prior art pump is disclosed in U.S. Pat. No. 3,285,182, granted Nov. 15, 1966, to Harry E. Pinkerton, and another representative prior art pump is disclosed in U.S. Pat. No. 3,814,548, granted June 4, 1974 to Warren E. Rupp.
Known small reciprocating pumps, however, require a priming action before the liquid can be pumped from the storage vessel. Larger reciprocating positive displacement pumps may have such a capability designed therein. More specifically, the larger pumps realize high ratios of displaced volume per stroke to the total volume of the conduits between the inner and outlet valves of said pumps. Such high ratios are unobtainable in known small reciprocating pumps for the conduits must be greater in size than the theoretical minimums if the pumps are to function satisfactorily. An alternative response to the priming problem is to connect the inlet side of the pump to the storage vessel in a liquid-tight manner, and to then manually or mechanically manipulate the vessel so that the liquid level within the drum is elevated above the inlet connection and the pump. The alternative response obviously calls for repeated handling of the storage vessel with attendant increased operating costs.